1. Field of the Invention
The present invention relates to a helical-blade fluid machine applicable to compressors, expansion machines, pumps, etc.
2. Description of the Prior Art
A helical-blade fluid machine has, in a closed casing, a cylinder and a roller piston eccentrically arranged in the cylinder. The peripheral surface of the roller piston has a helical groove in which a helical blade is inserted to define compression chambers in the cylinder. Relative motion between the cylinder and the roller piston draws coolant gas from an intake end of the cylinder into the compression chambers and successively conveys and compresses the gas toward a discharge end of the cylinder. The compressed gas fills the casing and is discharged outside.
Generally, the helical-blade fluid machine directly draws gas into a compression mechanism, compresses the gas therein, once discharges the compressed gas into the casing, and sends the gas outside through a discharge pipe attached to the casing. As a result, the casing must contain a high-pressure atmosphere. The compression mechanism intrinsically has a long axis that needs long bearings.
The compression mechanism is conventionally designed to partly submerge in a lubricant pool in the casing. This dissolved much coolant in the lubricant under the high-pressure atmosphere, thereby increasing the temperature of the lubricant and decreasing the viscosity thereto to improperly lubricate the long bearings of the compression mechanism.
The coolant may be an HFC-based high-pressure coolant, which has a very high saturation pressure. For example, the saturation pressure of R410A is about 1.5 times higher than that of conventional R22. The casing of the fluid machine must withstand such high pressure. Namely, the casing must have a thick wall, which increases the weight as well as cost of the fluid machine.
When the roller of the compression mechanism in the lubricant pool is driven, it stirs the lubricant, to destabilize the supply of the lubricant, thereby destabilizing the torque and total operation of the compression mechanism.